Switch mechanism



Dec. 11, 1956 J. A. MATHEWS 2,773,963

SWITCH MECHANISM Filed Jan. so, 195e -5 sheets-sheet 1 I Llf i 1 Nfl |||||1III |y||||||| MINIMUM Ilm I IWLIUWI 'n j MJ Dec. l1, 1956 YJ. A. MATHEWS 2,773,963

SWITCH MECHANISM Filed Jan. 30, 1956 5 Sheets-Sheet 2 J. A. MATHEWS SWITCH MECHANISM Dec. 11,A 1956 5 Sheets-Sheet 5 Filed Jan. 30, 1956 ma: M1

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Dec. 11, 1956 J. A. MATHEws SWITCH MECHANISM 5 Sheets-Sheet 4 Filed Jan. 30', 1956 Dec. 11, 1956 J. A. MATHEWS 2,773,963

SWITCH MECHANISM Filed`Jan. 30, 1956 5 Sheets-Sheet 5 Commercial Company,Y Cook County, Ill., a corporation of Blinois Application January 30, 1956, Serial No.`"562,312

14 Claims. ((1200-153) This invention relates to electrical switchingk means and particularly to a type of non-locking' switch mechanism adapted for use in' association with mechanisms for selective control of electrical or electronic equipment such as computers, musical instruments, servomotors, counting and packaging machines, etc.

` Certain of the more important features'of the invention are:

(l) The provision of a switch 'mechanism having extremely low inertia andhence suitable for'high speed operation.

(2) The provision -of a. switch` mechanism which permits accurate correlation between position ofactuator and operation of switch.

(3) The provision of a switchine'chanism having extremely low noise 'output when actuated.

(4) The provision of a kswitch `mechanism requiring very light pressure to operate and having the unique or unusual characteristic of allowing a large amount of overthrow or contact range with a scarcely perceptible 'buildup of contact pressre or actuator resistance.

(5) The provision of a switch mechanism'having both rotary and wiping action after initialcontact.

(6) The provision of a switch-'mechanism in vwhich both fixed and moving members experiencev a change of contact point after initial contact is made, thereby'distributing wear. v

(7) The provision of a 'switch mechanism having the features already mentioned plus the advantage of double contact points at all times with a single moving contact member. Y

(8) The provision of a switch mechanism of the vaforementioned type in which actuation pressure, contact pressures, transfer time, etc. can beaccurately and simply controlled.

(9) The provision of a switch mechanism having no contact bounce under high speed operation.

(l0) The provision of a switch mechanism which, because of the combination of features set forth in paragraphs 4, 5, 6 and others to be described later, is capable of an almost unlimited life and is not affected by fatigue of spring materials or overstress because of excessive motion.

(ll) The provision of a switch mechanismwhich, in combination with the above features, can be readily assembled in the proper housing Without fastening of any kind and be self-retaining by virtue of its own spring tension.

(l2) The provision of a switch mechanism having one or more of the above features in which any moving part may be easily replaced without too-ls and without dest|ruc tion of other parts.

(13) The provsion of a switch mechanism having means to automatically adjust itself to variable spacing between switch and actuating means, as well as to variable motion of said means.

(14) The provision of a switch havingn a chosen range of Contact as referred tothe motion of actuating means,

, 2,773,963 Patented Dec. 1,1., 1956 lCC and having theV ability toadjsti'tsl accordingly should said motion increase. l .1 l

(l5) The provisioniof aswiltch niechnistnwhih 4cannot be Ydamaged should 'irnj'ticin of acttingmns considerably exceed its'ri'rrrial limit. r

The above and'frthr objects 'ot invention 'will' be more readily understood by "th 'following "description of lone embodiment'tle'reoffthis being'a specific adaptation for use withan electronic ihusicalfiiist'runent 'operated by a keyboard,l such'aslsed onapi'ano, ij'g'an lor's described in the Matliwstet'al. "'tNo, 21,707,895,

Reference is 'made 5ito "the accompanying drawings wherein- Figs.5\toll-inclusive dw, y schein-atieillustrations, asequence -of "different \endi`tin'si`r`1`the voperation y'-f 'la single switch. t l 'l In earryingthe-i'nvention into practice fo'the specific -application aforementioned, use is 'made of aa fplurality of similar switches containe'dtin *ahousing-*consisting of a base plate'2 vland afcver'tl, which is'sectional fox-ease of access, as shown in Fig'stli' and 3.

Fastened to the ybaselfplate Zwby'm'eans of rivets or other suitable fastener, not shown to lavoid confusion, are in order-' a strip 'of insulating paper or=tape-3,-a strip of insulating-m-ateriai4 carrying suitable connecting lugs 12 and, finallyaratherintricate-molded-plastic piece 5 encompassing several switchesandiprovid-ing suitable barrier walls between switchesas well as allthe-supporting and containing-structurenecessary for -theswitches themselves.

To-each switch is attachedafngerg, intendedfor eX- ternal operation, which; passes through` thel felt dust -seal 14 `and protrudes through retangular holes' in thegcover l. The entire upper half of the housing shownin Fig.--2 is lleft vacant to provide space-forcable-and wiring.

Fig. 4 illustrates the essential-elements of lone for-m of the invention as used in lthe application described above. These elementsconsist ofa torsion 'coil 'spring 7, the contact member 9 and the actuator 8. A p I prefer to wind the Itorsionmspring 'l with afplurality of turns in order to achieve high lcompliance in a small space -and to permit awsubstantial 'angular rotation without sensible changeof force. l' O ne endv7 b ofthis spring is carried tangenti'ajllfy(` awaytrom` the `airis,-an'd'is'held vclown'by lug y1"2. UEitherthe-end 7b ofthe spring 'wire itself or lug 12 may Ybe iisedtor attaching an external connection. n y f The left-hand end""of sprn'gleaves the coil tangentially but is formed in a bend or hook 7a at its extremity a clockwise direction, as viewed from either end, to a certain tension.Y I prefer toform contact member 9 from one piece of wire and in a shape similar to a crank near one end, as shown at 9a and 9b inFig. di. This offset portion 9a extends under coil spring 7, but the straight portion of 9 passes over the hooked end 7a of 7, which, by virtue of winding tension, is always lifting upward.

The actuator 8 is preferably formed from comparatively heavy wire formed linto two parallel legs 8b and 8c, which l'prefer to produce by a U shape. One of these legs 8c passes freely through and acts as an axis and support for spring 7. Beyond the coiledportion of 7, leg 8c passes through journals or bearings 5a and 5b which support 8 and the spring body of 7 at a suitable height for free operation.

It should be understood that both ends of spring 7 are being held down-one end 7b by being trapped under lug12, and the other end 7a by contact member 9 which, in turn, is trapped under bus-bar or o contact element 10.` Since both ends of spring 7 are trying to rise because the spring is wound up in a clockwise direction but are prevented from doing so by 9 and 12 as previously explained, the net reaction on the coiled body of spring 7 isl a strong downward thrust which maintains actuator 8 firmly seated -in its bearings (which are open at top) without further restraint.

In the commercial form of the invention shown in all of the drawings, plastic molding provides the journals and supports 5a, A5b for 8 which also maintain spring 7 in loosely conned position, as well as barrier walls 5e which prevent excessive axialmotion of 8, and grooves lfor containing fixed contact bus-bars and 11 and maintaining them in accurate position with respect to each other and to the rest of the mechanism.

The two xed contacts of the switch represented in this embodiment by the bus-bars 10 and 11 are nove-l in that they are closely wound coil springs of small diameter with relationship to wire size, and they are wound with maximum initial tension between turns, which results in a spring of exceptional stiffness and straightness. These contacts 10 and 11 could be formed by grooving or threading solid straight wire as in co-pending application of Mathews and Mann, Ser. No. 466,738, or by knurling or notching strip or rod by means well known to those familiar with mechanical arts. Since contact member 9 is only loosely guided in a lateral direction by guide bosses 5c and 5a', it will always assume a position 4upon contact with either 10 or 11 in a trough between turns or peaks, resulting in two tangential contact points assuring low resistance vanddependable contact even under adverse conditions.

The distance between the bus-bars 10 and 11 minus the diameter of contact 9 determines the transfer o-r no contact distance in switch motion. In the particular device described herein it is desirable to keep this transfer 5 time to a minimum, hence the distance between bus-bars 10 and 11 is only .010" greater than the diameter of contact wire 9.

As already described, the hooked end 7a of torsion spring 7 is pressing upward on contact member 9. Referring to Figs. 4 and 13, it is seen that a position of stable equilibrium has been reached in the olf or relaxed position, since the upward pressure of '7a has been balanced by contact pressure of member 9 against busbar 10, and portion 9a against the under side of coil 7. Contact pressure of member 9 against bus-bar 10 will be a percentage of the pressure exerted by spring 7a at the junction A of 7a and 9. This percentage can be expressed as the ratio of distances In the commercial form of the invention described in these drawings, the f ront leg 8b of acuator 8 is shown resting on top of and intersecting contactor 9 at its approximate operating center, while point A is approximately 1/3 of the length of member 9 away from the common axis 8c. A downward pressure on 8 at point B of 1/3 less than pressure of 7a upward at point A will cause contactor 9 to reach zero contact pressure against bus-bar 10 and slightly more downward pressure at B will cause contactor 9 to leave bus-bar 10 and approach bus-bar 11. Up to this time, all motion has been rotary with the axis of rotation being Sc. However, the moment that member 9 contacts lower bus-bar 11 it can no longer move downward at the point of contact and this point becomes the fulcrum for rotation of member 9. Actuator 8 and hook 7a of spring 7 can only rotate about their common axis 8c, so that further motion of point B in a downward direction results in a more rapid depression of point A which now rotates at an angular velocity I/a greater than that of actuator 8, in effect winding up the spring 7 at a more rapid rate than indicated by the rotation of 8 about its axis. It should be remembered, however, that the number of turns of the coiled portion of 7 are such that even a large angular rotation :results -in 4a very small change in torsional force exerted at point A; thus a considerable motion downwards of point A is possible after Contact of member 9 with busbar 11 without noticeable buildup of contact pressure between member 9 and bus-bar 11. It is interesting to note that when switch was relaxed, pressure of member 9 on the upper bus-bar 10 was 1/3 the force exerted by torsion spring 7 at point A, While after transfer of movable member 9 to lower bus-bar 11 and going well beyond, the pressure on lower bus-bar 11 is still 1A; of torsion pressure at point A. This is true because the length of member 9 from point of engagement with busbar 11 to intersection with leg Sb is three times the distance from this intersection to point A. This is based on the assumption that the force exerted by spring '7 is constant throughout motion, which is approximately true.

The downward motion of 8 is terminated when point B strikes the bottom surface, which is also part of plastic molding 5. This limitation of motion is a requirement peculiar -only to the particular form of the invention illustrated in Figs. 1 to 4.

Figs. 13, 14 and l5 respectively show more clearly what happens to cont-act wire 9 during a cycle of operation similar to that just described. Fig. 13 shows switch in relaxed or olf position with member 9 in contact with .upper bus-bar 10 and portion 9a in contact with spring 7. Fig. 14 shows member 9 as it has just contacted lower bus-bar 11 but 9a still in contact with coil 7. Fig. 15 shows limit of downward or on motion, with member 9 still contacting bus-b-ar 11 but portion 9a flat against base at rear end under coil spring 7. Again referring to Figs. 13, 14 and l5, it is evident that the hooked end 9b of member 9, besides maintaining the longitudinal position of member 9, also -acts as a pivot for the odset portion 9a, causing axial rotation of member 9 as if it were cranked. This action twists the straight forward portion of member 9 after Contact thereof with bus-bar 11 only. This same rotary action also changes the point of tangency where contacter 9 touches bus-bar 11 and because of restraint of hook 9b changes the effective length of member 9 to point of contact with bus-bar 11. Thus, point of contact between contacter 9 and bus-bar 11 is never the same for either of these elements for any different point of the on range.

Another novel feature of this invention is n self-adjusting feature incorporated in the finger 6. This part could be made in several forms, but I prefer to make it of deal soft beryllium copper strip formed into a loop of small diameter near one end, as shown at B, and hardened after forming. The loop of finger 6 at B is slightly smaller than the diameter of wire from which actuator 8 is formed. After finger 6 is formed, it is heattreated at 600 1F. for'2 thourS, iat "whieh itimeit fhas ireached -a hardness comparable toispringsteel. Finger y6tislthenpressed*over the leg '8b o'f actuatorf -at point B, which itV grips with aforcepredeterminedby dimensionof looped port-ion-offfingerlthusprovidinga fric- -tion-grip which will retain a fixed :position relative `to actuator 8 unless the latter v.is held-and a force lin excess of affixed amount is -appliedlto theffree-end of'inger. dorreasons to be discussed later, -it vis important that `slippage occurat B before the forceapplied -tofree-end of 6 vcauses any `substantial orappreciable bending or springing of `the linger 6 itself. `For ybestperformance in lthe particular adaptation of the invention herein `dis -closedylinger and actuator-3 should be asrigid as possi- 3bleand -yet 'be light-imweight and possessed ofa relatively large surface at free end and at B. It is also important lto avoidcorrosion. -At the same time the-material `lfor parts andi-8 must beiductile `to permitisharp bending 'in 'for-ming. It is for 'the vforegoing freasons 'that I prefer -to use `an alloy of copper '-98% and beryllium 2% for `both "finger 6 andactuator '8.

LAOther essential parts oflthe ymechanistnfsuch as'7, '19, 10 and 11 ha-vethe same requirements pluslthe yadditional 3requirements of providing goodelectrical conduction and 1low contact resistance. Ialso prefer -toama-k'e -these elements of pretempered BeCu alloy -wire which yhas been pre-plated with a substantialsilvercoating-.during lwire drawing and therefore involves vno *treatment leither by lheat or electrolytic action after lfabrication. Actuator 8 is also preplated, since it is also an important electrical element of the switch and contact member. 'The silver coating is also very eective as a`lu`b1icant=for=friction lgrip -at point 1B. The silver-coating =at this point =pre vents gading, 'freezing and abrasion between lthe .two hardened pieces (finger f6 Vand actuator i8). '.lnaddition, ythe 'film ofsilver (which is very soft frelative `to BeCu alloy) maintains smooth land uniformtorque duringmany A`cycles ofrotation of clutch B.

Itwillbe noted that there is no solid connection between lug 12 andcontact member l9 but rthere are-two parallel paths of vcurrent low from to StZ-one said .pathibeing through actuator v8 which contacts 9 and, in turn, makes multiple pressure contact with the `coiled Lportion -of 7. Another path is by high lpressure conftact with vspring 7a at'point A. In practice, no trouble has been encountered `with this indirect method. In .this connection, it should be noted that all points of contact from :member 9 through to lug 12 are silver to silver -and .under considerably higherfpressure than `the switch contacttitself as provided between contactor'9 and busbars 10er-1I.

An important feature of the invention relates to the l.location of pivoting means for contact-member 9 y.either below or in close relationship to the common axis -Sc of members v7 and B. Taken together this relationship of relements provides little or no relative motion other :thanrolling between 8 and 9 .or at A, thus, reducing wear to a minimum at points of greatestrpressure.

It is assumed that little or no compliance or exing `takes place in Vfinger 6 or actuator 8 at any time, since such-action would result in point B (Figs. 4 and 6) strikfing base v5 every time the switch is actuated, as will be apparent from the following description. Y

So far in this description no .mention has been made of the reason for the slip clutch and self-adjusting feature between nger 6 and actuator 8 at B.

"In the introduction, mention was made of the specific usage of the commercial form of the invention` herein described by attacheddrawings. This usage requires the device to selectively control the tones of an electronic organ by the individual depression of the playing keys of arpialno keyboard. In this usage it is necessary that a unit consisting of a plurality of the switch elements herein described be placed under the keys of a piano and make contact to provide predetermined tones from which are `omitted for clarity. .stopld and cover 1 of Fig. 3 :are not'shown.

the organ Vwhen specic lpiano fkeys 'are depressed It is necessary that allaorgan 'notes `sound for fa :fixed -lpart offthe key-motion This ipart is commonlyp'referred to ibe fthe `last half of .the total. stroke.

Sincefiaconsiderable lvariation exists in the under sur- 'face of'woodenikeya their lowest point of motion ywhen .depressed 'and therelationship .of this point `to` mounting-surfaces beneath them, atconsiderable adjustment of couplingbetweenlkeysand switches must be provided in `order :to enable .a plurality of such switches to provide the same response .and playing range inpianos of many dilierent'makes and .evenbetween individual keys .of the samepiano.

:It is inconvenienttand .time-consuming totadjust v60 ormore individual switches to their respective keys, and even if this were done, wear of felt stops, etc. would in time increase thezp'laying time and overstress the switch or coupling.

.The present invention .provides automatic .self-adjustment .of :each iswitch and compensation for increasedmotion with age or wear, and :represents an improvement Aover method disclosedyin the Larseni Patent No. 2,714,- 145, sincepressure can never exceed the 'predetermined amount built into `friction, grip .vor-clutch at point B, and :no ubuild-up of pressure between inger 6 and key'takes place in normal Ioperation.

IReferenceis ynow made to Figs. -5 to l2 inclusive to illustrate the full cycle of operation of commercialy form of .the invention herein disclosed. In `the kinterest of clarity, Figs. 5 to l2 inclusive have .been skeletonized, changed :in scaleand all non-essentials removed. All-of .thesel'tigures.represent a vert-ical section through an individual switch mechanism which is now shown iniixed relationship tof-a scale of motion 13 `and pivot rll9-as sociated vwith :a'piano key I7 shown inpar'tial section. :The 'scale 218 shows the position `ot' thelkey by the pointed Vend .of fkey 17. .Number il indicates relaxed or non- 'playingposition which is also the highest. position vof key.

Number 8 corresponds to lowest position of key under heavy yfinger pressure. The limits of key motion corresponding to numbers 1 and 8 of scale 18 are determined :by stops offelt or similarresilient material 4associated with thekeyboardand which are not shown in the drawlngs.

Again referring to Figs. 5 through-l2, it should also be understood that legSc is supported in fixed position relative to 5 by the bearings or trunnions 5a and 5b of Fig. 4

In like manner, felt up- However, if "the `aforesaid upstop and'cover were shown in their yproper position, they would permit lifting of actuator 8 'only slightly above the horizontal.

Advantage is taken of this latter fact Ibefore installation of the switch assembly under the .keyboard by pull- Iing up on the left -or free end of iingers` 6 until they stand Vat lan langle of only 30 to 40 from the vertical when free. In doing this, linger (Fig. 5) is forced to rotate clockwise about actuator 8 4at clutch B, so that .before -ikey 17 is installed, the free endof linger 6 `would ibe much higher than shown'in F-ig. 5. Presuming that the preliminary adjustment just described has lbeen made, the mere installation of key 17 in place Ias shown :in Fig. 5 without depression will caus-e clutch B to "be driven down to base 15, causing contacter 9 to touch lbus-bar 11. .This causes the organ to play even though lkey |17 is at rest or lin 1a non-,playing pos-ition. In an instrument containing a plurality of keys :and switches, this condit-ion would result in simultaneous sounding Iof all notes.

Referring now to Fig. 6, however, wesee the key i7 depressed to the limit of its motion as it would be lin very hardplaying. This is Number 8 posit-ion onscale n18. This yiigure shows that no change has occurred in the :position or relation of elements 7, "8, 9, 10 or 11 of -rthe switch, butftuger 64 has been forced to rota-te counterclockwise about clutch lB until it .forms .an angle of only approximately 20 with the plane of actuator 8. This angle thenceforth remains unchanged.

Fig. 7 Ishows key 17 returned .to its relaxed or scale -l position. It will be noted that linger `6 has been lifted by action oi spring 7 on member '9 to its uppermost or rest position. IIt will not rise higher because contactor 9 has made contact with bus-bar 10, lwh-ich in common practice is grounded to silence ya signal or note source. It should also be noted that nger 6 'has not been able to -follow key l17 back to Number 1 position and that there is no longer physical contact between 6 and 17.

-F-ig. 8 represents the beginning of the second stroke of key 17. The key has been depressed to position 3 and has just re-established contact with finger 6. No change from Fig. 7 has taken place in the -switch mechanism and the note is still silent.

Fig. 9 shows key 17 at position 4 or Vs stroke. Contactor 9 has left ground bus-bar 10 and -is halfway to playing bus-bar i1-1. Spring 7, however, is still hold-ing oiset 9a up against coiled body of 7. No contact is being made so that note -does not sound.

Fig. `l() shows key 17 4at position 5 or 1/2 stroke. Contactor 9 has just touched playing bus-bar 11 and note is sounding. Relationship of elements 7, 8 and `9 to each other has not changed lin Figs. 7, 8, 9 and l0 and tall motion has been rotational about 8c as center.

Fig. 11 lshows key 17 in .position 6 or 3:/4 stroke. Contactor 9 has now begun to rotate about its point of contact lwith bus-bar 11 as reenter, thereby separating portion 9a for the rst time from coil of spring 7. This downward motion of Vsection `9a of contactor is accomplished by rotation `about hook 9b as center. Note still plays.

Fig. l2 illustrates the final or No. 8 position of key 17 at completion of stroke. Clutch B is at or near contact with base and all elements are in the same position as shown in Fig. 6, with contactor section 9a almost paralllel with base 5. Note still plays because contactor 9 is still incontact with bus-bar 11.

iA release of key 17 will restore all conditions -to those of Fig. 7 and the sequence of events depicted in Figs. 7 through l2 will be repeated every time the key 17 is depressed. If wear or packing of felt stops ipermits key 17 to go beyond position 8 after long use, clutch B will take a small additional set to compensate for the added motion, @but playing range (4 to t8) will remain constant with respect to bottom of stroke.

The design of cover 1 with its rectangular openings to felt 14 permits lingers 6 4to be depressed until `they are flush with said cover, effectively protectin-g the entire mechanism from accidental damage and permitting assembly to be used in very limited space. The over-all outside thickness, .for example, of the adaptation herein disclosed being only l/i.

II prefer to mold lbase 5 of nylon because of its resilience under impact, low lfriction characteristic as bearing material, inherent quietness and remarkable Wearing qualities, but this choice is not necessary or essential to the invent-ion disclosed herein. Anyone versed in the ant lw-ill readily appreciate that dimensions of elements and form of fingers maybe Varied to suit a wide range of actuating means and conditions.

While -I have described more or less precisely the details of construction, I do not wish to be understood =as limi-ting myself thereto, 4as I contemplate changes yin form, the proportion of parts and lthe substitution of equivalents as circumstances may .suggest or render expedient without departing from the spirit or scope of the invention.

What I claim as my inventionis:

l. An electrical switch mechanism of single pole single throw, =or ysingle pole double throw spring return type consisting of an organization of 1coactively relatedelements comprising la torsion spring wound in coil formg'a rigid actuator having two parallel extensions ot round cross section; a contactor of elongated form which is free to move within limits in a plane normal to the axis of the torsion spring but which is confined sufficiently in other directions to insure proper coaction with all other elements, iixed contact members suitably disposed about said contactor, and a at metallic, depressible, angular nger yhaving a portion coactive with one of said parallel extensions to `form therewith a .friction clutch enabling pivotal motion of the nger about the axis of said extension and a change in angular motion of the inger from a non-permanent angle to a permanent angle in response to downward press-ure applied a lirst time thereto.

2. A switch mechanism according to claim 41 wherein one extension of Ithe actuator is passed longitudinally through -th-e coil of the torsion spring xand -is of a diameter small enough to permit .t-ree rotation of the coil about said extension.

3. A switch mechanism according to claim l 'wherein one extension of the actuator :is passed longitudinally through the coil ofthe torsion spring and is of a diameter small enough to permit free rotation of the coil about said extension and wherein pivot and support means are provided Ifor Ithe actuator, said means also serving to limit the torsion spring .against longitudinal motion.

4. A switch mechanism according to claim y1 wherein the contactor is limited in motion near one of its ends by fixed contacts, the other end thereof being free to move principally in the direction of motion of the actuator, and means to limit said motion in one direction.

5. Mechanism according to claim 1 wherein means are provided by which motion of the actuator under pressure may be continued for a substantial distance beyond the point at which the contactor engages one of the fixed contacts, with no substantial increase of said pressure and with no substantial increase of pressure between said one fixed contact and the contactor.

6. A switch mechanism according to claim l in which means are provided enabling substantial excess motion of the actuator beyond the point of engagement of the contactor with one of said fixed contacts and wherein said excess motion is converted to both rotary and wiping action between surfaces of the contactor and said contact together with a continuous motion of said point of engagement on both the contactor and the contact.

7. An electrical switch mechanism of the single pole single throw or single pole double throw spring return type comprising a movable contactor, fixed contacts, a U-shaped actuator for conveying motion to the contactor and spring return means coactive with said contactor, said actuator including two sections, one of which is a vertically depressible metallic finger, coupled by a fraction grip to the other section and slips rotationally thereon upon application of torque to said grip in excess of that encountered in a first operation of the switch in response to depression of said linger.

8. A switch mechanism according to claim 7 in which means are provided including a stop to cause said friction grip to slip if motion greater than that required for intended operation of the switch is imparted to said actuator.

9. A switch mechanism according to claim 1 in which the actuator comprises two parts, one of which is formed of round wire and the other thereof of spring material formed to grip said first part under spring pressure and having a portion extending radially from said first part, thereby permitting mutual rotation of one of said parts about the other as an axis upon application of a torque to the grip in excess of that encountered in normal operation of the switch.

l0. A switch mechanism according to claim 1 wherein said fixed contacts each consist of round wire formed into a closely wound coil disposed at right angles to the movable contactor and wherein said contactor is formed of round wire.

11. A switch comprising a U-shaped member providing parallel spaced apart tirst and second portions and a connecting portion; means forming a bearing in which the rst portion of said member is mounted for tilting motion of said member; a stop, a contact, a rectilinear contactor respectively coactive with the stop and said contact; and a coil spring through which said first portion passes axially thereof, said spring being fixed at one of its ends and provided at its other end with an extension which engages said contactor and urges same against said stop.

12. A switch mechanism according to claim 11 wherein a motion imparting device is provided, the same having frictional engagement with the second portion of the U- shaped member and adapted for motion about the axis thereof, said device having a lever portion for application thereto of pressure for tilting said member and engaging said contactor with said contact.

13. A switch mechanism according to claim 11 wherein the extension of said coil spring is freely hooked under the contactor between the first and second portions of said U-shaped member.

14. A switch mechanism according to claim l1 wherein the contactor extends from said -stop to a point adjacent to said coil spring at which point it is formed at an angle to the axis of said contactor and pivoted at a location removed from said axis.

References Cited in the file of this patent UNITED STATES PATENTS 1,444,557 Sachs Feb. 6, 1923 1,796,612 Nagl Mar. 11, 1931 2,089,081 Wemple Aug. 3, 1937 2,666,822 Pelletier et al Jan. 19, 1954 

